Forage harvesters of the type to which the present invention pertains employ relatively heavy and large rotatable cutter head having a plurality of knives thereon which are spaced even distances circumferentially around the cutter head. Normally, said knives are arranged upon the periphery of the cutter head at an angle to the axis thereof as well as at an angle to the shear bar, it being understood that the shear bar normally is mounted stationarily within the harvester in parallel relation to the periphery of the cutting head, whereby during the shearing operation, no sudden shock is imposed upon the knives of the cutter head or the shear bar as occurs when the rotatable knives and shear bar as occurs when the rotatable knives and shear bar are mounted in parallel relationship to each other. Also, said knives preferably are skewed in order to dispose the cutting edges thereof within the circumferential cylindrical outline of the cutter head in order to have the cutting edges of the knives operate in shearing manner with the relatively straight cutting edge of the shear bar.
It is also conventional at present to include in a forage harvester of the foregoing type a power-driven, rotatable grinding wheel as part of the standard equipment of said harvester. Guide means are also included adjacent the periphery of the cutter head along which the grinding wheel is moved in grinding relationship relative to the knives. When the guide means is disposed parallel to the shear bar and the axis of the cutter head, the grinding wheel will be positioned to grind the cutting edges of the knives. However, in order to complete the sharpening operation, it is necessary to grind a bevel surface immediately rearward of the sharpened cutting edges, said bevel being slightly concave in cross-section and the same preferably is of uniform depth and width along the full length of the knives.
For purposes of minimizing the inventory of knives for such cutter heads, it has been found that when, for example, the same knives are used on cutter heads which respectively are of eighteen inch and twenty four inch diameters, problems arise with respect to grinding the bevels on the knives immediately rearward of the cutting edges. This is especially found to exist when knives originally manufactured for a cutter head of eighteen inch diameter are employed upon a pg,3 cutter head having a twenty four inch diameter. Thus, it has been found that when the foregoing situation exists, and the guide for the grinding wheel is left in its parallel position with the shear bar after sharpening all of the cutting edges of the knives, and each knife then is individually ground by the grinding wheel to re-surface the bevel rearwardly of each cutting edge, the bevel is substantially wider at one end of the knife than at the other and is preferred that the bevel be of uniform width along the entire length of each knife so as to provide a shearing surface of uniform width on the cutting edge of each knife. Accordingly, the present invention has been devised to permit the use of one type of knife on two different diameters of cutter heads and also enable the grinding wheel of the forage harvester to not only sharpen the cutting edges but also grind bevels of uniform depth and width rearward of each cutting edge, by means described hereinafter.
To provide an understanding of the details of the type of forage harvesters to which the present invention pertains, attention is directed to prior U.S. Pat. Nos. 3,751,859 in the name of P. K. Pederson, dated Aug. 14, 1973; 3,793,792 in the names of R. A. Wagstaff and T. W. Waldorp, dated Feb. 26, 1974; and 3,863,403, in the name of P. F. Fleming, dated Feb. 4, 1975. In all of these previous patented structures, grinding wheels and means to guide the same are illustrated but none of them propose solutions to the problem which is solved by the present invention, namely, providing guide means for skewed knives which are made for one diameter of cutter head and are employed on a cutter head of a different and especially a larger diameter, and still be able to grind a bevel surface of uniform depth and width along the full length of each knife.